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JOURNAL  OF  A«llTiAL 

DEPARTMENT  OF  AGRICULTURE 


VOL.  v 


WASHINGTON,  D.  C.,  OCTOBER  18,  1915 


PARASITISM  OF  COMANDRA  UMBEtl/ATA 


By  GSORGE  G.  HE;DGCOCK 


rnc .  -  borefctry .  Main  Library 

• 


PARASITISM  OF  COMANDRA  UMBELLATA 

By  GEORGE  GRANT  HEDGCOCK, 

Pathologist,  Investigations  in  Forest  Pathology, 

Bureau  of  Plant  Industry 

One  of  the  most  important  and  most  injurious  of  the  stem  or  blister 
rusts  occurring  on  pines  is  Peridermium  pyriforme  Peck,  which  attacks 
Pinus  (murrayana)  contorta  Loud.,  P.  ponderosa  Laws.,  and  P.  ponderosa 
scopulorum  Engelm.  in  the  western  United  States,  P.  divar-icata  Du  Mont 
de  Cours.  in  the  Northern  States,  and  P.  pungens  Michx.  and  P.  rigida  Mill, 
in  the  Northwestern  States.  Peridermium  pyriforme  is  a  heteroecious 
rust  and  is  dependent  for  its  existence  upon  its  alternate,  or  summer, 
stage,  which  occurs  on  species  of  Comandra. 

The  problem  of  the  eradication  of  this  important  rust  being  so  inti- 
mately associated  with  plants  of  Comandra  spp.  led  the  writer  to  investi- 
gate their  manner  of  growth  and  means  of  propagation.  It  was  found 
that  the  plants  of  at  least  two  species,  C.  pallida  A.  DC.  and  C.  umbellata 
(L.)  Nutt.,  have  apparently  become  largely  dependent  on  parasitism 
for  their  continued  existence.  The  other  two  North  American  species, 
C.  limda  Richards,  and  C.  richardsiana  Fernald,  resemble  the  former 
species  in  appearance  and  habit  and  are  probably  equally  parasitic  in 
their  nature. 

The  writer  has  carefully  examined  the  root  system  of  living  plants  of 
both  C.  timbellata  and  C.  pallida,  but  only  of  dried  specimens  of  the  other 
two  species.  The  former  have  long  underground  rootstocks  which  bear 
here  and  there  small  roots  or  rootlets  usually  less  than  5  inches  in  length. 
These  rootlets  branch  sparsely  and  are  nearly  always  attached  to  the 
roots  or  underground  stems  of  other  species  of  plants.  At  the  point  of 
attachment  there  is  formed  by  the  root  of  Comandra  spp.  a  nearly  hemi- 
spherical disk  or  holdfast.  This  holdfast  is  either  superficial  or  slightly 
embedded  in  the  cambium  layer  of  tissues  of  the  host,  but  does  not  send 
out  haustoria,  as  is  the  case  in  species  of  Razoumofskya  on  the  limbs 
and  trunks  of  coniferous  trees.  The  chief  function  of  the  roots  of 
Comandra  spp.  appears  to  be  that  of  attachment  to  host  plants  for  the 
purpose  of  obtaining  nourishment  and  a  water  supply.  Plants  of  Coman- 
dra spp.  frequent  dry,  rocky  soils,  which  often  have  a  low  water  content. 

Plants  of  all  these  species  of  Comandra  bear  leaves;  and  although 
attached  as  parasites  to  the  roots  of  other  plants,  they  are  not  entirely 
dependent  upon  their  host  plants  for  organic  compounds,  since  they  are 
able  to  further  elaborate  these  compounds  in  the  liquids  received  from 

Journal  of  Aricultural  Rsearch.  Vol.  V,  No.  3 

Dept.  of  Agriculture,  Washington,  D.  C.  Oct.  18,  1913 

ag  G — 60 

(133) 


-'-95966 


134 


Journal  of  Agricultural  Research 


Vol.  V,  No.  3 


their  hosts.  In  this  respect  their  development  is  similar  to  that  of 
plants  of  species  of  Phoradendron. 

Both  C.  umbellata  and  C.  pallida  very  commonly  are  associated  with 
and  parasitic  upon  species  of  Vaccinium,  but  are  not  at  all  dependent 
upon  this  genus  for  host  plants.  This  has  especially  been  noted  in  the 
case  of  C.  pallida  in  the  States  of  Colorado,  Montana,  Nebraska,  South 
Dakota,  and  Wyoming,  and  in  C.  umbellata  in  the  States  of  Con- 
necticut, Maryland,  Michigan,  Minnesota,  New  Jersey,  New  York, 
Pennsylvania,  Vermont,  Virginia,  and  Wisconsin,  and  the  District  of 
Columbia.  Plants  of  both  species  are  parasitic  upon  a  great  variety  of 
plants  belonging  to  widely  different  sections  of  the  Spermatophyta. 
No  attachment  to  plants  of  any  member  of  the  Pteridophyta  has  been 
noted. 

C.  umbellata  has  been  found  by  the  writer  as  a  parasite  on  the  roots 
of  the  following  species  of  plants  in  the  Eastern  States : 


Acer  rubrum  L. 

Achillea  millefolium  L. 

Andropogon  -virginicus  I/. 

Angelica  villosa  (Walt.)  B.  S.  P. 

Antennaria  plantaginifolia  (L.)  Richards. 

Aster  ericoides  L. 

Aster  macrophyllus  I/. 

Aster  patens  Ait. 

Aster  undulatus  L. 

Baptisia  tinctoria  (L.)  Br. 

Betula  nigra  L. 

Betula  populifolia  Marsh. 

Car  ex  sp. 

Castanea  dentata  (Marsh.)  Borkh. 

Chimaphila  umbellata  (L,.)  Nutt. 

Chrysopsis  mariana  (L.)  Nutt. 

Comptonia  peregrina  (L.)  Coulter. 

Danthonia  compressa  Austin. 

Fragaria  americana  (Porter)  Britton. 

Fragaria  -virginiana  Duchesne. 

Gaylussacia frondosa  (L.)  T.  and  G. 

Hieracium  "venosum  L. 

lonactis  linariifolius  (I,.)  Greene. 

Lespedeza  molacea  (L.)  Pers. 

Lysimachia  quadrifolia  L. 


Meibomia  paniculata  (L.)  Kuntze. 

Panicum  sp . 

Poa  compressa  L. 

Poa  pratensis  L. 

Populus  tremuloides  Michx. 

Potentilla  monspeliensis  I/. 

Quercus  coccinea  Muenchh. 

Quercus  digitata  (Marsh.)  Sudw. 

Quercus  marilandica  Muenchh. 

Quercus  nana  (Wood)  Britton. 

Rhus  copallina  L. 

Rosa  blanda  Ait. 

Rosa  canina  L. 

Rubus  canadensis  L. 

Rubus  procumbens  Muhl. 

Rubus  -villosus  Ait. 

Solidago  bicolor  L,. 

Solidago  caesia  L. 

Solidago  juncea  Ait. 

Solidago  nemoralis  Ait. 

Solidago  speciosa  Nutt. 

Spiraea  salicifolia  L. 

Vaccinium  atrococcum  (A.  Gray)  Heller. 

Vaccinium  nigrum  (Wood)  Britton. 

Vaccinium  vacillans  Kahn. 


In  addition  to  the  foregoing  and  incomplete  list  there  must  be  added 
at  least  three  unidentified  species  of  grasses. 

During  the  last  three  years  a  number  of  attempts,  with  varying  suc- 
cess, have  been  made  at  Washington,  D.  C.,  to  grow  plants  of  C.  um- 
bellata and  C.  pallida,  both  by  germinating  the  seed  and  by  transplanting 
rootstocks  to  beds  and  pots  in  greenhouses.  In  every  case  where  living 
rootstocks  unattached  to  host  plants  have  been  transplanted  to  pots  or 


oct.is,  1915  Parasitism  of  Comandra  umbellata  135 

beds  without  the  host  plants  present,  little  or  no  growth  on  the  part 
of  the  plants  of  Comandra  spp.  has  taken  place,  and  the  plants  eventually 
died.  Successful  results  in  growing  these  species  have  been  accom- 
plished by  only  two  methods:  First,  by  transplanting  sods  containing 
the  plants  of  Comandra  spp.  from  out  of  doors  to  the  greenhouse  with- 
out breaking  the  attachments  of  the  roots  of  the  parasite  to  those  of 
the  host;  second,  by  planting  seed  in  flats  in  the  fall  out  of  doors  and 
germinating  them  in  the  presence  of  the  roots  of  host  plants  after  ex- 
posing the  seeds  to  freezing  temperatures  by  allowing  the  flats  to  remain 
out  of  doors  all  winter. 

Dr.  E.  P.  Meinecke,  of  the  Office  of  Forest  Pathology,  reports  by  letter 
that  he  has  three  plants  of  C.  umbellata  raised  from  seed  sown  in  1913, 
which  remained  dormant  till  1915,  when  they  germinated  and  grew 
without  any  host  plant.  These  plants  were  5  inches  high  on  July  17, 
1915.  This  is  positive  proof  that  this  species  of  Comandra  can  live 
without  parasitism  if  necessary.  It  remains  to  be  seen  whether  these 
plants  will  continue  to  grow  indefinitely  without  the  presence  of  host 
plants. 

The  results  from  our  experiments  indicate  that  when  the  rootstocks 
of  plants  of  Comandra  spp.  are  broken  entirely  loose  from  their  root 
attachment  to  host  plants  they  usually  die  through  an  inability  to  re- 
attach  themselves.  These  new  data  on  a  subject  which  apparently  has 
not  been  previously  investigated  indicate  a  greater  degree  of  parasitism 
in  species  of  Comandra  than  has  hitherto  been  suspected,  and  will  render 
more  obvious  the  desirability  of  the  destruction  of  plants  of  Comandra 
spp.  in  the  vicinity  of  forest-tree  nurseries. 


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